1. Field of the Invention
The invention relates, in general, to a bicycle frame that is aerodynamically shaped, lightweight, and stiff, including a main frame structure and front fork assembly, and in particular to the integral tension configuration, integral outer shell, integral tension struts, and integral tension ribs used in its construction.
2. Description of the Prior Art
Known prior art includes both traditional frame design, using traditional construction techniques and materials, and more recent innovative frame design, using new construction techniques and materials.
Traditional frame design and construction were developed under relatively limited availability of materials. As steel was readily available, cost effective, and relatively easy to form into simple structural shapes, round steel tubes were found to be the most efficient structural element to use in bicycle frame manufacturing. The construction technique used included the cutting and fitting of these tubes, and brazing them together at their joints with or without joint lugs.
Since traditional frame design, was developed primarily under the availability of round straight steel tubes, it primarily employed a two triangle design, with a rear triangle to carry rider load, and to hold the rear wheel, and a front or main triangle that also carried rider load and joined the rear triangle to the head tube and front fork thereof, and a front fork made of steel tubes. This was known as the safety bicycle.
From a structural standpoint the traditional two triangle design is essentially a very simple, short, open web truss. The top tube acts as a top boom, the down tube and rear wheel stays act as a bottom boom, and the seat tube and seat stays act as inclined interconnecting members between the top boom and the bottom boom, as in a typical open web truss of a bridge, for example.
A typical open web truss is comprised of a top boom, a bottom boom, and inter-connecting vertical and/or inclined members between the two. When a vertical load force is applied to such an open web truss, the top boom is subjected to resultant compression forces, and the bottom boom is subjected to resultant tension forces, while the interconnecting members used to resist compression and sheer forces between the upper and lower booms may employ a combination of compression and tension members.
FIGS. 1A and 1B illustrate the similarities between the two structures by way of side view diagrams, and the directions of operative tension and compressive forces by arrows, with arrows pointing away from each other representing tension, and those point towards each other representing compression.
The simple open web truss that comprises the bicycle frame structure of the two triangle design is supported at each end with the axle of the wheels, in a way similar to a bridge truss abutment; indirectly through the front fork in the front end, and directly in the rear. When a rider load is applied to the top of the bicycle it causes the top tube and seat stays to go into compression, and the down tube and rear wheel stays to go into tension, while the seat tube, and seat stays act as inclined compression and shear resistant members.
The compressive and tensile strength characteristics of steel tubes, their availability and cost, and their workability, made them highly suitable for the two triangle design, and conversely made this design a very efficient and practical configuration, and most builders still use it with minor variations in the frame geometry.
Round steel tubes also work well to resist lateral and torsional flexes, and their ability to do so can improved by such things as adding flutes, internal rifling, double and triple butting, and increasing their diameter. Such increases in strength were sought to improve performance and allow weight reduction.
An essential structural feature of this design, however, is that is includes vertical and inclined members, and their postures limit their ability to receive significant aerodynamic improvement, even though attempts were made to do so by reducing frontal area, by using oval and tear drop tube shapes, reducing front wheel size, sloping the top tube, and so on.
So, even though the traditional two triangle design has desirable features in stiffness, weight, and vertical load bearing capability, its limitations in aerodynamics, as well as the need for speed in the area of competitive cycling, have driven on the search for more aero-dynamically efficient configurations.
Other materials that have become more available, such as aluminum, titanium, and fiber reinforced composites, have provided builders with the opportunity to attempt new and innovative designs, that reduce frame weight and may offer significant improvements in aerodynamic efficiency.
While some bicycle frame builders have merely substituted tubes made of these materials for steel tubes, and gluing or welding of the joints in place of brazing in the traditional two triangle design, others have used new materials, in particular, fiber reinforced composites, to produce new bicycle frame designs which are aerodynamically far superior.
While some of these new frames have greatly improved aerodynamics with their streamlined shapes and efficient configurations, they have the reputation of being heavy, flexible, and/or bouncy, and thus are thought to have greatly reduced riding characteristics compared to traditional steel frames. One reason for this is that some of these frames are, primarily, variants of the open web truss type construction, and employ traditional load bearing engineering principles. In addition, some of these innovative designs sometimes require complicated and costly construction techniques, as well as extensive mechanical adjustments. A superior design should address the aerodynamic efficiency, stiffness, strength, and weight requirements, of a bicycle frame simultaneously.
In view of the above it is the aim of the present invention to achieve singularly and simultaneously:
the production of a bicycle frame of which the configuration, shape, and arrangement of appropriate parts is inherently suited for aerodynamic efficiency;
the production of a bicycle frame that is extremely strong, stiff and resistant to flex or deflection under applied vertical, lateral, and torsional loads without heavy self weight, and consequently;
the production of a bicycle frame that is very light weight in proportion to its strength, and finally;
the production of a bicycle frame that is simple to construct and easy to assemble. To achieve these ends it was necessary to invent and develop a new load carrying and transferring structural schema, called the integral tension configuration.
The present invention, therefore, discloses a bicycle frame that makes use of said integral tension configuration, and discloses said integral tension configuration itself, and its structural subcomponents, namely an integral tension outer shell, an integral tension strut, and an integral tension rib, wherein the multidirectional tensile strength of said structural subcomponents as well as their arrangement are the primary structural characteristics used to produce the strength and overall stiffness of the structure under applied vertical, lateral, and torsional loads. The coessential structural subcomponents defined as integral tension struts and integral tension ribs are used, wherein the multidirectional tensile strength characteristics of said struts and ribs are the primary load transferring component. The said bicycle frame includes a main frame structure and fork assembly; said main frame structure including an airfoil shaped xe2x80x9cdown tubexe2x80x9d running from a fork mounting means that may be comprised of a head tube sleeve and steer tube combination to a crank assembly mounting means that may be comprised of a bottom bracket sleeve with two streamlined rear wheel stays running from said airfoil shaped down tube at said crank assembly mounting means or bottom bracket area to center of rear wheel, and an airfoil shaped xe2x80x9cseat tubexe2x80x9d emanating from said airfoil shaped down tube between said tube sleeve and said crank assembly mounting means or said bottom bracket sleeve at a midway point, and employing airfoil shaped gussets at their common joint, and including a bicycle saddle mounting means; and said main frame structure being composed of an aerodynamically shaped outer shell and inner structural members, preferably including, but not limited to, a various number of generally parallel and lineally running integral tension struts along or near the midsection of said airfoil down tube, said rear wheel stays, said airfoil seat tube, that affix along said integral tension struts entire predetermined circumferential edge to the inner surfaces of the said outer aerodynamic shell, and possibly, but not necessarily a various number of integral tension ribs generally perpendicular to the upper and lower of the said generally parallel and lineally running integral tension struts, and bonding to the upper and lower inner surfaces of the said aerodynamic outer shell or said integral tension struts; said inner structural members and surfaces of the said aerodynamic outer shell or said integral struts; said inner structural members and said outer aerodynamic shell, preferably, but not necessarily, made of fiber reinforced composite laminates and arranged for efficient collaboration to carry rider load and resist flex, such as side and torsion flexes, reduce frame weight, and increase strength; said main frame structure also including said fork mounting means, preferably consisting of a head tube sleeve and steer tube combination, said crank assembly mounting means that may be comprised of bottom bracket sleeve, a bicycle saddle mounting means such as a seat tube sleeve and binder bolt combination, at the top of said airfoil seat tube, and rear wheel mounting means, preferably consisting of rear wheel receptors affixed to interior or exterior of said main frame structure at the end of said rear wheel stays; said fork assembly including a fastening means to said main frame, preferably consisting in a steer tube, headset bearing race support, and may include a fork crown, two front wheel support structures or blades running from said fork crown to the center of front wheel, and front wheel mounting means that may be comprised of receptors which are affixed to the interior or exterior of the end of said fork blades opposite said fork crown, said fork blades being composed of an airfoil shaped outer shell and inner structural members, including, but not limited to a various number of generally vertical and parallel lineally running integral tension struts affixed along said integral tension struts entire circumference to the inner surface of the said outer airfoil shell, and said fork blades permanently affixed to said steer tube and said possible fork crown. Both said main frame and fork are integrally constructed and form structural frame units that are aerodynamically efficient, lightweight, and strong. Other advantages, features, characteristics, and details of the present invention will be apparent from the following description in conjunction with the accompanying drawings, in which like reference numerals designate the same or similar parts.